There are two basic groups of such adjustment devices. The one group is known, for example, from published, non-examined European patent application 0 324 184. In this group of adjustment devices the valve is disposed in the piston. In the other group of adjustment devices, as for example known from U.S. Pat. No. 3 656 593, the valve is disposed in that end of the housing which is opposite the side where the piston rod exits. Both types of adjustment devices are at least partially filled with gas, by means of which, when the valve is opened, the piston rod can be pushed out of the housing or it can be pushed back in against the force of its pressure. If the piston itself is slidable in a fluid-filled chamber, then a complete, i.e., for all practical purposes rigid, arrestment of this adjustment device, which can also be called a gas spring, becomes possible. If, however, the entire housing is filled with pressure gas, a spring potential having a very steep space-force curve is possible, even with the valve closed. The pressure in the housing of the respective adjustment device is very high and amounts as a rule to 80 bar, but it may also be much higher. In order to keep the adjustment devices functioning a long time, seals must be provided that will effectively prevent a flow of pressure medium to the outside on a long-term basis. These seals must simultaneously be highly resistant to wear, since, depending on the use of the adjustment device, movements arise to a large extent between the seal and the piston rod on the one hand and between the seal and the trigger pin on the other hand. Polyurethane has, for example, proved very reliable as a sealing material highly resistant to wear. When such adjustment devices are used in an aggressive environment, i.e. even in the case of high atmospheric humidity, it has been found that the seals preventing a flow of pressure medium to the outside are destroyed in too short a period of time, which amounts to a destruction of the entire adjustment device.